Creep Alarm Calculations
There are four variations of the Creep alarm calculation. These alarm calculation types can only be implemented with the CygNet Enhanced Point Scheme. See Understanding the CVS Metadata File for more information about the elements and attributes that define a CygNet Point Scheme.
See the following subsections for details:
The number of entries stored for this calculation is specified by the histvaluecount attribute in the CvsMetadata file for a CygNet Enhanced Point Scheme.
For more information, see Alarm Calculation Types.
Creep Average
The Creeping Average alarm uses the Creep Average (CREEP_AVG) calculation. On each update, the system will calculate the average from the newest value older than the time interval to (and including) the previous value. The system compares the difference between the average and the update value, and sets the alarm bit if the difference is more than the threshold value.
The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Creeping Average alarm using the Creep Average calculation type:
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Alarm Calculation Configuration — Creeping Average |
Calculation Parameters
The calculation parameters for this alarm are user-provided. The threshold value is always specified as a positive number, although it can be specified as a negative number if that makes sense in the calculation.
- Maximum Engineering Units Threshold (calcparm1) — maximum difference allowed between average and updated values.
- Time Interval (sec) (calcparm2) — time interval in seconds.
Preliminary Calculations
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Sum = sum of previous values within time interval + newest value older than time interval
Count = number of summed values
Average = Sum/Count |
Equation
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ABS(Average Value - Current Value) = difference in value |
- If difference > calcparm1, alarm is set.
- If difference ≤ calcparm1, alarm is not set.
Example
- calcparm1 = 10
- calcparm2 = 60
In this example, the Creeping Average bit (CONFIG8) is set because the difference of the average (183.51) and the current value (105.2) is greater than the calcparm1 value of 10.
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Sum = 917.59 Count = 5 Average = 183.51
183.51 (Average) - 105.2 (Current) = 78.318 (value is greater than calcparm1 value of 10) |
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Alarm Calculation Results — Creeping Average |
Creep Value
The Creep (Value) alarm uses the Creep Value (CREEP_VAL) calculation. On each update, the system calculates the change in value between the current value and the newest value older than the time interval. There is a comparison made between the difference and the calcparm1 value, and if the absolute value of the difference exceeds the threshold value, the alarm is set.
The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Creep (Value) alarm using the Creep Value calculation type:
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Alarm Calculation Configuration — Creep (Value) |
Calculation Parameters
The calculation parameters for this alarm are user-provided. The threshold value is always specified as a positive number, although it can be specified as a negative number if that makes sense in the calculation.
- Maximum EU Difference Allowed (calcparm1) — maximum allowed change of value over the specified time interval before the alarm is set.
- Time Interval (sec) (calcparm2) — the time span used to determine the difference of the two values.
Equation
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ABS(Current Value - Newest Value Older than Time Interval) = difference in value |
- If difference > calcparm1, alarm is set.
- If difference ≤ calcparm1, alarm is not set.
Example
- calcparm1 = 10
- calcparm2 = 30
In this example, the Creep (Value) bit (CONFIG12) is set because the difference in value between the current value (16.25529) and the newest value older than the time interval (1) is greater than the calcparm1 value of 10. If the value increases or decreases by more than 10 in 30 seconds, the bit will be set.
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16.25529 - 1 = 15.25529 (more than the max change of value allowed, so alarm bit is set) |
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Alarm Calculation Results — Creep (Value) |
Creep Value Positive
The Creep Value Positive alarm uses the Creep Value Positive (CREEP_VAL_POS) calculation. On each update, the system will calculate the engineering units change from the newest value older than the time interval, and set the alarm bit if the difference is more than the threshold value specified.
The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Creep (Value Pos.) alarm using the Creep Value Positive calculation type:
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Alarm Calculation Configuration — Creep Value Positive |
Calculation Parameters
The calculation parameters for this alarm are user-provided. The threshold value is always specified as a positive number, although it can be specified as a negative number if that makes sense in the calculation.
- Maximum EU Difference allowed (calcparm1) — maximum allowed change of value over the specified time interval before the alarm is set.
- Time Interval (sec) (calcparm2) — the time span used to determine the difference of the two values.
Example
- calcparm1 = 10
- calcparm2 = 30
If calcparm1 is 10 and calcparm2 is 30, and if the threshold value increases by more than 10 in 30 seconds, the bit will be set.
Creep Value Negative
The Creep Value Negative alarm uses the Creep Value Negative (CREEP_VAL_NEG) calculation. On each update, the system will calculate the engineering units change from the newest value older than the time interval, and set the alarm bit if the difference is less than the threshold value specified treated as a negative number.
The following image shows the area of an Analog Alarm Settings page of a PNT Editor with an enabled Creep (Value Neg.) alarm using the Creep Value Negative calculation type:
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Alarm Calculation Configuration — Creep Value Negative |
Calculation Parameters
The calculation parameters for this alarm are user-provided. The threshold value is always specified as a positive number, although it can be specified as a negative number if that makes sense in the calculation.
- Maximum EU Difference Allowed (calcparm1) — maximum allowed change of value over the specified time interval before the alarm is set.
- Time Interval (sec) (calcparm2) — the time span used to determine the difference of the two values.
Example
- calcparm1 = 10
- calcparm2 = 30
If calcparm1 is 10 and calcparm2 is 30, and if the value decreases by more than 10 in 30 seconds, the bit will be set.
